Telephone system



AJuly 26, 1932. c. E. LoMAx TELEPHONE SYSTEM Filed oct. 24, 1930 2 Sheets-Sheet `1 m.N\ n@ @VIR mmv/Ml! "Ir-@E15 l Ellarancza E. L Umax 2 Sheets-Sheet 2 Inuen nr Elarence E. Lomax Patented July 26,1932

N UNITED. STATES PATENT OFFICE CLARENC E. LOMAX, OF` OAK PARK, ILLINOIS, ASSIGNOR, BY MESNE ASSIGNIYCENTS, TO

ASSOCIATED ELECTRIC LABORATORIES, ING., OF CHICAGO, ILLINOIS, A CORPORATION y F DELAWARE y'irinnienonn SYSTEM Application filed October 24, 1930. Serial No. 490,869.

This invention relates to telephone systems in general, particularly to toll service trunking arrangements for enabling toll operators to set up connections to subscribers lines.`

It is the usual practice in modern telephone systemsto route all outgoing toll calls to a recording operator who determines then/ants of thecalling subscribers. Under certain conditions this operator will complete a conil nectionV to the wanted'line while the calling subscriber waits. If for any reason it is irnpractical to complete the connection in this manner the operator tells the calling subscribed to hang up his receiver and that he will be calledwhen the desired party has beensecured. A ticket will be made out in either case, of course, andfin the latter case this ticket will be passed rto a @elayed Call operator. The Delayed Call operatorwill then attempt to establish a connection with the wanted party and, when such connection has been obtained, will set up a new connection to the subscriber who originated the call. In automatic telephone systems this new connectionwill be extended over av special-toll switch train which is generally similar'to the local switch train, but is adapted to prof vide greater transmission eiiiciency and more complete supervision. Incoming toll calls likewise will be extended over this toll switch train.

In the pastby far the greaterperc-entage of outgoing toll calls were handled on the delayed basis, and only calls to nearby towns were completed without delay. The ratio between delayed and non-delayed calls has gradually changed with improvements in the equipment and in operating methods until, atthe present time, it is estimated that approximately 90% ofall originating` tollcalls are completed on a non-delayed basis. Trafs fic over the toll switch train has consequently been reduced accordingly.

The toll switch train as now provided con'- sists essentially of transmission selectors, intermediate selectors and toll connectors. The number of switches required depends both on the volume of trailic and upon the interconnecting arrangements used, thatl is, upon the physical limitations imposed by the design of the switching apparatus. The toll switching apparatus ordinarily provided in a typical exchange .with an ultimate capacityof ten thousand lines, for example, will consist of a group of toll transmission selectors, each of which terminates `a trunk from the tollV switchboard. These selectors will have access over each of the ten bank levels to a group of intermediate selectors, each of which serve A a group of one thousand lines. Each group of intermediate selectors in turn lhas access to ten groups of connectors7 that is, one group of connectors for each group of one hundred lines. Y i

Under present operating conditions, that is, with the majority of originating toll calls completed on a non-delayed basis, it has been found that one or two connectors are sufficient to handle 'the incoming and delayed toll calls `for the average `hundred lin-e group. On this basis it may reasonably be assumed that seven or eight intermediate selectors will be sufficient to handle thetraiiic for a one thousand line group. The toll switch train as'at pre-sent manufactured and installed is not adapted to operate most efficiently under the above traliic conditions, which'may be considered average. In the first place there will be two or three unused sets of bank contacts and their associated cabling in each` .inherent in prior systems, such as discussed.

-rlllietrunking arrangement contemplated by the invention is designed in accordance with the `present day requirements and results in a large reduction in the amount'of unused bank terminals and cabling. This arrangement constitutes one of the main features of the invention. Another feature is the novel wiper selecting arrangement whereby the two-digit transmission selector is enabled to select either of two idle trunk lines. Another feature is the arrangement for giving the transmission selector direct access to the connectors of each hundred line group thereby eliminating entirely the intermediate selectors. Still another feature is th-e pro- Vision of signal selecting apparatus in the transmission selector itself Vrather than in the connector. This latter arrangement permits the use of a simple connector switch which is very desirable since connectors will obviously outnumber the selectors of the preceding rank in all cases. y

The foregoing features together with others not specifically mentioned will be discussed in more detail in connection with thedescription of the operation of the various circuits involved, reference being had to the accompanying drawings comprising Figs. 1 and 2. The drawings show by means of the usual circuit diagrams suliicient apparatus in a telephone system embodying the invention to permit the invention to be readily explained and understood. Fig. 1 shows a toll operators cord circuit CG and a toll trunk line terminating in a toll transmission selector TTS. Fig. 2 shows a toll connector C and a subscribers line and substation T.

Referring now to Fig. 1, the cord circuit CC, of which only a part is shown, may be of any suitable type commonly used for toll service. The calling device CD is common to a number of cord circuits and is connected to the particular cord circuit shown by means of the key K. The toll trunk line shown terminates at the toll switchboard in the manual jack J and at the automatic switchboard in the transmission selector TTS. This selector mechanically is of the well known Strowger Vertical and rotary type and is arranged to be directively operated in both its vertical movement and its rotary movement. The selector is provided with two separate sets of wipers which cooperate with corresponding sets of contacts in different banks. The corresponding contacts of the different banks incidentally terminate trunks extending to connectors of the same hundred line group. The particular set of wipers used is determined by the busy or idle condition of the respective contact sets. Associated with the selector is an auxiliary ringing current selecting switch RS. The auxiliary switch is of the well known type used in multi-party connectors and is commonly referred to as a minor switch. It will be appreciated that there may be as many transmission selectors and associated trunk lines as are required to handle the traffic, and that the banks ofthe selectors will be multiplied in the usual way. Referring now to Fig. 2. Connector C, mechanically and electrically, is similar t@ the ordinary Strowger party-line connector switch except that no ringing current selecting switch or ring-cut-off relay is provided. This connector, in common with a similar toll connector and the usual local connectors, has access to a group of subscribers lines of which the line extending to substation T is shown. Substation T may be of the usual type provided in automatic telephone systems. The subscribers line also terminates in the usual lineswitch (not shown) over which outgoing connections are extended by way of the local switching apparatus.

Having briefly described the invention and the various circuits, the operations involved in setting up a connection from the toll switchboard to substation T will now be described in detail. The call in this case may be either a delayed call or an incoming call since the operations involved are the same in either case. It will be assumed that the operator has selected the cord circuit CC to extend the connection and that the plug P is inserted in the jack J of the trunk line extending to transmission selector TTS. A loop circuit is thereby Completed extending from battery, lower winding of impulse relay 106, contacts 148 and 132, upper lefthand winding of the repeating coil, trunk conductor 1, ring contacts of the jack and plug, normally closed contacts 6 and .12 of key K, winding of polarized relay 3, normally closed contacts 8 and 5 of key K, tip contacts of the plugand jack, trunk conductor 2, lower left-hand winding of the repeating coil, and contacts 138 and 181 to ground. Polarized relay 3 does not operate in this circuit due to the direction of the current flow. Relay 106 operates and at contacts 158 completes a circuit for release relay 107. Relay 107 operates, connects ground to the local holding circuit at contacts 160, prepares the impulsing circuit at contacts 161, and opens a point in the circuit of the release magnet at contacts 162.

The operator now actuates key K to the right, thereby bridging calling device CD across the talking strands of the cord circuit in place of relay 3. The calling device is then operated in accordance with the first digit of the wanted number and the previously traced loop circuit for relay 106 is opened intermittently at impulse contacts 10 of the calling device. Relay 106 responds in the usual way by deenergizing and reenergizing in accordance with the digit dialled. Relay 106 upon restoring the first time completes the impulse circuit which may be traced from ground, contacts 159, 161, and 175, normally closed off-normal spring contacts 121, winding of relay 108, winding of vertical magnet 160 to battery. Relay 108 and the vertical magnet operate, the latter 'raising the wipers of the switch one step.

The off-normal springs operate on the first 'vertical step'of the wipers andjthefremaining impulsesv ofifthe` first series are transmitted .through relay 8 and theV vertical' magnet by way of contacts 122: and 164. vRelay .108 is a slow-to-release relay and remains operated throughout vthe series of impulses. Relay 108 uponoperating completes a circuitA at contacts 168 for relay 108., Relay 108 op crates, opens `points in the ringing circuit at contacts 141 and 145, and completes a locking circuit for its `upperwinding by way of contacts 148'and 151. Shortly after the last impulse of the series relay 108 restores and transfers the impulsing circuit to relay 109 and rotary magnet 117 by way of contacts 165. A

The operator now dials the second digit and relay 106I responds as in the previous case. The groundA impulses are transmitted over the previously described impulse circuit to relay 109, and rotary magnet 117. Relay -109 Operates in series with the rotarymagnetand, dueto'its slow-to-release characteristic, remains cperatedthroughout the series of impulses. Magnet 117 respondstogeach im! pulses ofthe series andsteps thewfipers of .the-selector aroundto the position: determined by the digit dialled. Relay 109 uponcperating, opens a-point inft'l'ie test circuit at contacts 4166 and at contacts 167 closes a circuit for relay 118. `Relay llf8operates, closes a circuit -forfrelay 114 at contacts 185, `and opens a point in the circuit of relay 110at conta-cts 187.A -Relayf114 operates, closes a point in the circuit of relay 112 at contacts 188, and closes a point in the circuit of relay11'0at contacts 189. Wipers 20:7212 of the .selector have beenpositioned on contacts terminating trunk linese'xtending to the required hundred line group, onegof-,whichfor example may be the trunk linecomprising conductors 218-215 terminating in connector C. Incase lthe trunk line terminating Yin the contactsfengaged by the-upper set of wipers is busy, the test contact thereof will be maikedibusy by the transmission selecto-rengaged in the'connecaion. `When relay 109restores, yshortly after the last'impulseoftheseries, a circuit will there- `fore be closed from thetest Contact, wiper 208, conductor 202, contacts 166; and 170, winding offrelay 115 to-battery. VRelay 115 upon o-perating willdisconnectfthe upper set of wipers atcontacts 190, 198, and 196 and at contacts `191, 194,and 195 will connect up the lower set of wipers. Relay 115 iwill also close aV point in its own locking `circuit at contacts 192 which will be completed subsequently by relay110. In case the trunk termin ating. in the lower `set of contacts engaged by the wipers is also busy, ground on thetest contact by way of wiper 211, conductor 205, contacts 194, 178, and 178, winding of relay 111. to battery willoperate relay V11.1. Relay 111 will complete a locking circuit for itself at contacts 177, openal point in the circuitvof relay 112 at contacts 179, and at contacts 180'will connect busy tone and ground to the lower trunk conductor to inform the calling operator that no idle connectors are available at this time.

In case the trunk line terminating in the 7T3,70

upper set of contacts is busy but that terminating in the lower set of contacts is idle, the operation will be as follows: Relay 115 will operate from the ground encountered on the test contacts by wiper 208 and the lower set 'fi-i5 of wipers will be connected. up as inthe previous case. Since the contact engaged by wiper 211 will not be marked busy in this case, relay 111 will not operate. It may be n noted that the foregoing test operation takes place immediately following the release of vrelay 109. Relay 109 upon restoring opens the circuit of relay 118 and relay 118 on restoring opens the circuit of relay 114. Both relays 118 and 114 are slow-to-release so that C relay 118 restores a short time after the release of relay 109, and relay 114 in turn restores a short time after the release of relay 118. .TNhen relay 118 restores under the above conditions, a circuit will be closed by "im way of contacts 186, 188, and 179 for relay '112. Relay 112 operates, completes a lock,- ing circuit for itself at contacts 182, disconnects the iinpulsing circuit previously described vfrom the rotary magnet at contacts 95 184, and at contacts 188 transfers this circuit to stepping magnet 124 of auxiliary switch RS. The apparatus is now in condition to respo-ndfto the third or ringing current selecting digit as will be described in connection 10 Under the. e conditions 105 before relay 114 restores a circuit is closed by 110 waryl of contacts 186, 188, and 179 for relay 112. 'Relay 112 operates, locks to ground at `cont-acts 160 by way of contacts 182 and connectsup the stepping magnet of the auxiliary l 'switch at contacts 188.

i `The third digit is now dialled and relay 106 responds kas in previous instances and transmits impulses over the local impulse circuit to magnet 124 of the auxiliary switch. VThe magnet operates in the usual way to advance 120 itswiperi n accordance with the digit dialled and wiper 126 accordingly comes to rest on a contact connected with ringing current of a particular frequency required to signal the wanted subscriber. Relay 109 operates in series with the stepping' magnet of the auxiliary switch and completes the circuit for relay 118, which in turn completes acircuit for relay 114. Relay 109 will restore shortly after thelast impulse of the series followed by 13 the restoration of relays 113 and 114 and before relay 114 restores a circuit will be completed from ground by way of oE-normal contacts 123 which close on the first step of 'E the auxiliary switch wiper, and contacts 187,

ilo

189, and 170 for the lower winding of relay 110. Relay 110 operates, completes a looking circut for itself at contacts 171, disconnects relay 115 at contacts 170, connects ground to the test wiper at contacts 172, opens the impulsing circuit at contacts 175, and closes the talking conductors of the switch through to the line wipers at contacts 168 and 176.

It may be noted at this time that the seized trunk line is not marked busy during the interval between its-seizure and the complete operation of the axuiliary switch. It is therefore possible that the same trunk may be occupied by a similar transmission selector at this time. Vhen this occurs the auxiliary switches of both transmission selectors will be operated, but the one operated iirst will get the trunk in the manner described. Since relay 110 in operating connects ground to the test wiper, the other selector attempting to take this trunk will be switched over by ground on the testl contact following the restoration of its series relay, which connects up the wiper switching relay of that switch. In case the lower trunk engaged by the second mentioned selector is also busy, the busy test relay of the switch will be operated as is the usual case and at contacts 170 will prevent the operation of the corresponding relay 110 of the second switch. The fact that the auxiliary switch is connected up will have no effect inasmuch as relay 110 cannot operate` and the operator using the second switch will receive busy tone in the usual manner.

ln case the lower trunk engaged by second switch is idle the trunk will be seized and the setting of the auxiliary switch will determine the party signalled.

Then two selectors simultaneously attempt to connect with the last trunk in the above manner the switch whose auxiliary switch is first set will seize the trunk by the operation of its switching relay 110. The trunk will be marked busy by ground on the test contact and the other switch attempting to seize this trunk will be prevented from doing so by the fact that the ground on the test contacts will operate the busy relay thereof which in turn will open the circuit of the associated switching relay, such as 110. The operator calling by way of the second switch consequently receives a busy signal.

Returning now to the normal operation involved in the seizure of the trunk comof relay 110 of the transmission selector, as

previously described, completes a circuit whichl may be traced from battery, upper winding of relay 221 of connector C, contacts 258 and 242, conductor 213, wiper 207,

conductor 201, contacts 190, 168, 157, 153, and 142, upper-right-hand winding of the repeating coil, contacts 134, upper winding of polarized relay 101, lower-right-hand winding of the repeating coil, contacts 144, 156, 176, and 196, conductor 206, wiper 209, conductor 215, contacts 248 and 263, lower winding of relay 221, to ground. The direction of current flow over the circuit is such that the two windings of relay 101 oppose each other, the lower winding of the relay having been energized in series with resistance 127 by way of olf-normal contacts 119 which closed when the transmission selector was operated from its normal position, and consequently relay 101 does not operate vat this time. Relay 221 of the connector operates, completes a circuit by way of contacts 260 and 234 for relay 222. Relay 222 operates, closes a point in the testing circuit at contacts 237, prepares the impulse circuit at contacts'238, and opens a point in the release magnet circuit at contacts 239.

The operator now dials the fourth digit and relay 106 of the transmission selector responds as before. Since the local impulsing circuit is open at contacts 175 no further stepping operations take place in the selector. The previously traced loop circuit for relay 221 is opened intermittently, however, at contacts 157 and the dialled impulses are thus repeated to relay 221 which responds accordingly. On the first release of relay 221 a circuit is closed from ground, by way of contacts 260, 235, and 238, normally closed olf-normal spring contacts 232, winding of relay 223, winding of vertical magnet 228 to battery. Relay 223 and the vertical magnet operate in the usual way. The magnet raises the wipers one step and relay 222 now completes a new impulsing circuit by way of contacts 240 and olf-normal contacts 233 which close on the first vertical step of the wipers. Succeeding impulses of the series are transmitted over this new circuit to further operate the vertical magnet and position the wipers of the switch opposite the called level. Relay 223 is slow-to-release and remains operated throughout the series of impulses. Shortly after the last impulse of the series, relay 223 restores and transfers the impulsing circuit by way of contacts 241 to relay 226 and the'rotary magnet in series.

The operator now dials the last digit of the called number and impulse relays 106 and 221 respond as before. Impulses are now transmitted over the circuit which now eX- tends by way of contacts 241, winding of relay 226, contacts 245, winding of rotary magnet 229, to battery. The rotary magnet operates -tostepthe wipers around t the contacts of the called line which in this case will be assumed to'bel the line comprising conductor `267-269. Relay 226 "operates in series with the rotary magnet and, due to its slow-releasingcharacteristics, remains operated throughout the series of impulses. Relay 226 connects test wiper 265 through to busy test relay 225 at contacts 254, and at contacts 256 completes a V"shunt circuit around contacts 251 0f the busy relay tor prevent that relay from interferringv with the iinpulsingas vthe wiperspass over busy contacts. Y Y

'Incase the called line is jbusy, wiper 265 will encounter a busy potential and relay 225 will operate in the usual way. TWhen relay 226 restores after the last impulse of the series, relay 225 will remain locked to ground at contacts 237 -by way of contacts 250 and 255. Relay 225 will open the'inipulsing circuit-at contacts 251, and at contacts 252 will apply a busy'tone to the lower talking conductor of the switchto inform the operator that-the called line is busy.

In case the called line is idle, wiper 265 will find -no busy potential and relay 225 consequently will `not operate. When relay 226 restores shortly after the last impulse of the vseries the test wiper will be connected through tothe lower winding of relay 224 and that relay will operate from battery through the cut-'off relay of the lineswitch associated with the called line. Relay 224 on operating completes a locking circuit for itsup'per winding at contacts 244, opens the circuit-to the `rotary magnet at contacts 245 prepares a circuit'fo'r relay 227 at contacts 246, and by Opening contacts 242 and 243 and closing contacts 243 and 247 the connection of relay 221 to the trunk conductor is reversed. The direction of current llow over the trunk line is accordingly reversed and polarized relay 101 of the transmission selector operates as its two windings lnow assist each other. Relay 101 on operating bridges both windings of relay 106 across the toll trunk lines so that current flow thereover is reversed by opening contacts 132 and 138 and 'closing contacts 133 and 139. Relay 101 also completes a locking circuit for itself by shunting resistance 127 at contacts 136, disconnects its own upper winding from the loop extending" to the connector by opening contacts 134, at contacts 135 and 137, bridges battery feed relay102 across the loop to the connector, and at contacts 133 and 137 bridges ringing current responsive relay across the tolltrunk line in series with condenser v150'. Since the connection of relay 221 of connector C to the trunk line has been-reversed ythe lower grounded winding will be connectedto theupper trunk conductor to whic'hthe upper or grounded winding fbat'teryffeed relay 1020i? theY transmission selector has been connected. Relay 221 consequently deenergizes and at contacts 236 completes a circuit for relay 227. Relay 227 operates, disconnects the talking conductors or the connector from relay 221 and connects them through to wipers 264 and 266 at contact-s 259 and 262, respectively. Relay 227 also applies direct ground to test wiper 265 atl contacts 261 to mark the line busy to other connectors. lt will be noted at this time that the talking conductors of the two switches are extended through clear without condensers or bridges aside from the battery feeding bridge at the transmission selector. Referring now to the cord circuit the operator upon completing the dialling of the .vanted number will restore key K to normal again bridging polarized relay 3 across the trunk line. Since, as previously explained, battery flow over the toll trunk line has been reversed by the operation or relay 101, relay 3 consequently operates and completes a cir- Y cuit at conta-cts 13 for lamp L. The lamp glows to indicate to the operator that the connection has beenvextended to the subscribers line.

To signal the called subscriber the opera-l tor actuates key K to the left thereby applying ringing' current to the toll trunk line t0 operates relay 100 of the transmission selector. Relay 100 completes a circuit at contacts 149 for relay 105. Relay 105 on operating opens the locking circuit for relay 103 at contacts 151, and at contacts 154 completes aV local holding circuit including resistance 130 for impulse'relay 106. Relay 103 restores and opens a point. in its own locking circuit at contacts 143 so that onthe restoration of key K to normal the relay will not reoperate. Ringing current is now applied to the upper talkingconductor over a circuit which may be traced from generator GEN, contact of auxiliary switch RS, wiper 126, lower winding of relay 103, contacts 141, 153, 157, 168, and 190, conductor 201, wiper 207, conductor 213, contacts 247 and 262, wiper 266, line conductor 269, through the bells and condenser at the called substation, conductor 267 wiper 264, contacts 259 and 243, conductor 215, wiper 209, conductor 206, contacts 196, 176, 156, and 145 to ground. Ringing currentV and battery are alternately connected to this circuit by interrupter relay 199 which alternately opens and closes contacts 197 and 198. The called subscriber is thus signalled intermittently. When the called subscriber answers, a direct current loop is closed at the called substation` and relay 103 operates, opens the previously traced ringing circuit at contacts 141 and 145, completes a locking circuit for itself at contacts 143, and extends the talking conductors through to the battery feed relay at contacts 142 and 144. Battery feedrelay 102 operates over the called subscribersloop and at contacts 140 completesA a circuit for relay 104. Relay 104 disconnects relay 106 from the toll trunk line at contacts 146 and 148, and at contacts 147 completes a local holding circuit includingresistance 130 for the relay. The disconnection ot relay 106 from the toll trunk line permits relay 3 of the cord circuit to restore and extinguish the lamp L, thereby informing the operator that the call has been answered. The operator may talk with the called subscriber by operating key K to connect the usual telephone set across the talking conductors of the cord circuit, and the call may be extended over the other end of the cord in the usual way to a toll line as required.

At the termination of the call the called subscriber will replace his receiver thereby opening the loop over which relay 102 is energized. Relay 102 in restoring opens the circuit of relay 104 which restores and reconnects relay 106 tothe toll trunk line. The reconnection of relay 106 to the trunk line reoperates relay 8 which again completes a circuit for lamp L. Lamp L glows, indicating to the operator that the called subscriber has hung up and that the connection may be released. The operator if necessary may recall the subscriber by again applying ringing current to the toll trunk line whereon the operation of relay 100 and the release of relay 108 takes place as previously described.

To release the connection the operator withdraws plug P from the jack thereby openingr the circuit of relay 106 which restores and opens the circuit of relay 107. Relay 106 also opens the loop circuit extending by way ot contacts 157, although this is without eiliect at this time since the impulsing relay of the connector has been disconnected from the circuit. Relay 107 on restoring removes ground from the local holding circuit at contactsv 160 which ground in turn has been applied to the test wiper and release trunk conductor to hold up switching relay 224 of the connector. Relay 107 also completes a circuit for the release magnet by way of contacts 159, 162, and olii-normal contacts 120 which closed on the first vertical step of the wipers. Release magnet 118 opt j erates to restore the switch wipers to normal position in the usual way. In the connector switch, relay 224 releases when ground is removed from the release trunk conductor and opens the circuit of relay 227. Relay 227 rej stores and connects ground by way of contacts 260, 285, 239, and oit-normal contacts 231 to release magnet 230 which operates to restore the switch wipers to normal position.

The operations involved in extending a. call over the lower set of wipers of the transmission vselector are substantially the same as those above described, except that relay 115 of selector TTS will be operated.

What is claimed is:

1. A toll switch train comprising toll selectors each adapted tobepositioned on its banks by two directive digits, and toll connectors arranged in groups according to the groups ot subscribers lines accessible thereto, all connectors of any one group being accessible in the same bank position of said selectors.

2. A toll switch train comprising toll selectors each adapted to select a sub-group of a particular group of trunk lines responsive to two series of digit impulses and to automatically select an idle trunk line of the subgroup, and toll connectors for each sub-group adapted to connect with subscribers lines.

3. A toll switch train comprising toll selectors adapted to select a sub-group of a particular group of trunk lines responsive to two series of digit impulses, to automatically select an idle trunk line of the sub-group, and to select a source of ringing current to be connected to a subscribers line responsive to a third series of digit impulses, and toll connectors for each sub-group adapted to connect with subscribers lines.

4. In a selector switch adapted to perform group and sub-group selection responsive to two series of digit impulses, automatic means for selecting an idle trunk line of a sub-group, and means responsive to a third series of digit impulses for selecting the ringing current to be applied to a called line.

5. In a. telephone system, a toll switchboard, a. toll selector, an auxiliary ringing current selecting switch associated with said selector, means controlled from the switchboard for operating said selector to select a toll connector, for operating said auxiliary switch to select a source of ringing current, and for operating the selected connector to extend a connection to a called line, and

means controlled from the switchboard lfor causing said selector to apply ringing current from the selected source to the called line.

6. In a telephone system, a switching mechanism adapted to respond to two directive digits to select any one of a plurality of groups of trunk lines and to automatically select an idle trunk line of the group, and an auxiliary switch associated with the selector adapted to respond to a subsequent directive digit to select any one of a plurality of sources of signalling current.

7. In an automatic switch, an impulse relay adapted to respond to each series of digit impulses representing the digits of a called number, contacts on said relay for repeating the impulses or" the first three series to the primary magnet of the switch, the secondary magnet of the switch, and the stepping magnet of an associated auxiliary switch respectively, and other contacts on said relay for repeating subsequent impulse series to succeeding switches.

8. In a telephone system, an automatic switch adapted to beoperated in its primary and secondary movements, respectively, by two directive digits to select a group of trunk lines, means in the switch for automatically selecting an idle trunk line in the group, an auxiliary switch associated with said lirst switch, and means responsive to the selectionof the idle trunk line for renderingA said auxiliary switch operable by a succeeding directive digit. i Y i.

9'. In a switchin mechanism adapted to be positioned -in selective relationship with a group of trunk lines responsive to digit impulses, means for automatically selecting an idletrunk line ofthe group, and means responsive onthe `receipt of further dialled impulses for effecting the seizure and lbusy marking of theselected trunk line.

10. In an automatic switch, means responsive to directive control by a calling party for positioning the switch in selective relationship with a group of trunklines, means for automatically selecting an idle trunk line in the group, and means `responsive to the exercise of further directivecontrol by the calling party. for causing the selected trunk line to be marked busy.

l1. In a telephone system, automatic switches adapted to be directively operated into selective Vrelationship with a group of l trunk. lines, automatic means in each switch for selecting an idle trunk line in the group without rendering the same unselectable to other of said switches, and means in each switch operated responsive to a further directive operation for causing the. associated switch to render said trunk line unselectable to other of said switches.

12. In a telephone system, an automatic switch, means in the switch directively controlled by a calling party for positioning the switch in selective relationship with a group of trunk lines, means in the switch for automatically selecting' an idle trunk line. in the group and for withholding busy marking potential from the trunk pending the exercise of further directive control by the calling party,

and means in the switch for automatically selecting a different idle trunk line in the group provided the first trunk line selected is seized and marked busy in another connection before the exercise of said further directive control.

' 13. In a telephone system, an automatic A switch adapted to respond to three seri-es of 1 digit impulses, means eective after the receipt of the second series of impulses for causing said switch to select an idle trunk line, and means elective after the receipt of the third series of impulses for causing the switch to seize the selected trunk line and to mark the saine busy.

14. In a telephone system, an automatic switch and an associated auxiliary switch, means for transmitting two directive digits to said first switch to cause the same to select a group of trunk lines, automatic `means in the lirst switch forselecting an idle trunk line in the group, means for transmitting a third directive digit to said first switch to operate said auxiliary switch, and means responsive to the completion of the operation of said auxiliary switch for causing said rst switch to seize the selected trunk line and to mark the same busy. i

15. In a telephone system, an automatic switch, directively controlled means for operating the switch into `selective relationship with a groupv of trunk lines, automatic means for selecting an idle trunk line in the group, directively controlled means associated Vwith said switch for selecting a source of signalling current, and `means effective on the completion of said last selective operation for causing` saidswitch to seize the selected trunk line and to mark the same busy.

16. In an automatic switch, means vdirectively controlled by a callingparty Jfor positioning the switch in selective relationship with a group of trunk lines, means for automatically selecting an idle trunk line ofthe group Iwithout marking the same busy until further directive control is exercised by the calling party, means for causing said switch to hunt for another idle. trunk line provided the trunkline iirst selected is marked busy before the .exercise of said further directive control, and means Vfor returning a busy tone to the calling party provided no other idle trunk line is available in the group.

17. In an automatic switch, means responsive to digit impulses for positioning the switch in selective relationship with agroup of trunk lines, automatic means for selectingcan idle. trunk line. of the group without marking the same busy until an additional digit Vimpulse is received, means for causing the switch to select another idle trunk line when the trunk line first selected is marked busy in another connection prior to the receipt of said additional digit impulse, and means for connecting up a' busy tone when the. trunk line last selected is also marked busy in another connection prior to the receipt of said additional digit impulse.

18.` In a Vtelephone system, an automatic switch terminating a trunk line, means for directively operating the switch to set the` wipers in engagement with a group of outgoing trunkv lines accessible ma particular position of the bank, means in the switchv for automatically testing successive outgoing trunk lines of the group untilV an idle one is -found while maintaining the wipers in the set position resulting rom said directive operation, means in the switchforseizing saidfirst idle outgoing trunk line and for repeating directive impulses thereover, and means fin the `switch-'operated when no idle outgoing trunk lines are available in the group forapplying a busy tone to saidirst trunk line while maintaining the wipers in the set position resulting from said directive operation.

19. In a telephone system, a toll selector repeater equipped with a plurality of sets of wipers, a group of trunk lines terminating in toll connectors accessible to said selector repeater, said group comprising a trunk line for each of said sets of wipers, means for directively operating the selector repeater to set the wipers on said group of trunks, wiper switching means in the selector repeater for automatically selecting an idle trunk line of the group while maintaining the wipers in said set position, and means in the selector repeater for repeating directive impulses over the selected trunk line to operate the associated toll connector.

20. In a telephone system, an automatic switch, a relay energized responsive to the directive operation of the switch to complete a control circuit which is extended to a succeeding switch on the completion of the operation of said first switch, means in the first switch for interrupting said circuit to directively operate the succeeding switch,

and means for deenergizing said re-lay to interrupt said circuit and to apply signalling current thereto.

2l. A toll switch train comprising a toll selector adapted to select a particular group of trunks responsive to two series of digit impulses and to automatically select an idle trunk in the group, and a toll connector terminating the selected trunk for extending connections to subscribers lines.

22. The combination with a toll selector having two sets of wipers adapted to be operated to a particular bank position responsive to two series of digit impulses, of two connectors accessible in said bank position, and means for rendering one or the other of said wiper sets eiective depending on which of said connectors is idle.

'23. A toll switch train comprising a selector having a plurality of sets of wipers which are set on a particular position in the banks responsive to the receipt by the selector of two separate series of impulses, and

for connecting up one of said sets' of wipers to select an idle one of said trunk lines, and means for repeating controlling impulses over the selected trunk line.

25. In a selector repeater, a plurality of sets of wipers, directively controlled means for moving said wipers in two planes to a particular bank position in which alike plurality of trunk lines are accessible, means for connecting up one of said sets of wipers to select an idle one of said trunk lines, means for repeating impulses over the selected trunk line to extend a connection, and means for applying signalling current to the trunk line.

26. In a telephone system, a selector, connectors, a called line, means for operating the selector to select an idle one of the connectors, means for operating the connector to extend a connection to said line, two sources of signalling current, signalling means in the selector for connecting one of said current sources to the called line, means for disabling said signaling means, and means in the selector for connecting the other of said current sources to the called line while said signalling means is disabled.

27. In a telephone system, a selector, connectors, a called line, means for operating the selector to select an idle one of the connectors, means for operating the connector to extend a connection to the called line, a ring cut-oil' relay in the selector, means for applying ringing current to the called line through a winding of said relay, means for operating said relay to disconnect the ringing current, and means in the selector for reapplying ringing current to the called line independent of said relay.

In witness whereof, I hereunto subscribe my name this 21st day of October, A. D. 1930.

CLARENCE E. LOMAX. 

